Process of tanning with malonaldehyde or succinaldehyde and optionally mineral tanning agent and leather produced thereby



, r 2,851,329 Patented Sept. 9, 1958 PROCESS OF TANNING WITH MALONALDEHYDE R SUCCINALDEHYDE AND OPTIONALLY MINERAL TANNING AGENT AND LEATHER PRODUCED THEREBY Ludwig Seligsberger, Newton, Mass., assignor to the United States of America as represented by the Secrotary of the Army No Drawing. Application November 18, 1&55 Serial No. 547,872

18 Claims. (Cl. 8-94.26) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein, if patented, may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to the art of producing leather from a hide, by tannage with a dialdehyde having at least three carbon atoms in the molecule, at a controlled pH range below 7, preferably within a pH of about 2.5 to about 5.

I have found that a hide which is tanned with an aqueous solution of a saturated aliphatic dialdehyde having at least three carbon atoms in the molecule, such as malonaldehyde (CHO.CH CHO) or succinaldehyde (CHO.C H .CHO) yields a plump and pliable leather resembling vegetable-tanned leather, provided the pH of the tanning solution is controlled to values below 7, preferably between about 2.5 and about 5. The aliphatic dialdehyde containing aqueous solution may be either preformed prior to immersion of the hide, or may be formed in situ, e. g., by immersing an acid pickled hide in an aqueous solution of a chemical capable of being hydrolyzed to form the desired aliphatic dialdehyde by reaction with the acid contained in the pickled hide., While it has been known in the prior art that glyoxal (CHO) may be used as a leather tanning agent at a pH above 7, say 7.5 or higher, I have found, surprisingly, that it cannot be used successfully for leather tanning under acid conditions, e. g., at pH 2.5-5, inasmuch as the resulting leather is boardy and stilf.

'I have also found that if malonaldehyde or succinaldehyde are substituted for glyoxal, but without pH control of the tanning solution to below 7 during the tanning process, the resulting leather is substantially stilfer and less plump than is the case when the pH of the tanning solution is maintained below 7 (say between 2.5 and 5) during the entire tanning process; neither does the leather, when treated with malonaldehyde or succinaldehyde at a pH exceeding 7 during all or a substantial part of the tanning process, possess the feel and appearance of vegetable-tanned leather, in contradistinction to leather treated in accordance with the teaching of my invention, i. e., at a pH below 7.

I have further found that dialdehyde tannage, in accordance with the present invention, can be accomplished in one or two days, even on a heavy steer bend, while vegetable tanning requires weeks. I have found also that the clialdehyde tannage in accordance with my invention can be combined with mineral tannages, such as chrome, aluminum, or zirconium tannages. The mineral tanning compounds can be applied either directly with the dialdehyde or as a separate operation. The mineral tanning agent may be added before or after the aldehyde, to the same bath, in which the aldehyde tannage proceeds or in a separate tanning operation.

" I have also found, surprisingly, that adequate tanning can be accomplished in accordance with my invention, by using as little as approximately 5%10% tanning material based on the dry weight of the hide substance, as compared with approximately 25% of vegetable tanning materials on the same basis. I have further found, surprisingly, that malonaldehyde gives a yellowish and succinaldehyde a light tan colored leather, the latter being a most desirable shade because of its resemblance to artificially bleached vegetable leather. Without committing myself to any particular theory for the explanation of these phenomena, I suggest that this may be due to a polymerization in situ of the higher dialdehyde (whose CHO groups are separated from each other by at least one carbon atom) on the leather fibers during the tanning, due to the maintenance of acidic conditions throughout the process, and without adding other polymer-forming agents. Leather thus produced has the desirable characteristics of plumpness, pliability, porosity, and soft feel resembling vegetable leather; the plumpness is particularly surprising in view of the light weight of the leather. Because of this light weight and porosity, the leather treated in accordance with the present invention is substantially superior to that of mineraltanned (e. g., aluminum-tanned or chrome-tanned) leather, and thus lends itself to impregnations with various impregnants, e. g., water-resistance-imparting and/ or abrasion-resistance agents, which is important from the military as well as civilian standpoint. On the other hand, leather in accordance with the present invention does not stand in need of large amounts of oils or greases, e. g., conventional fat-liquoring or stutfing ingredients, for the purpose of attaining pliability at normal temperatures; this eliminates an important drawback of ordinary fat-liquored or stuffed leather which stiffens at low temperatures because of congelation at arctic temperatures of the oils and greases used in fat-liquoring and stufling.

While, as pointed out, my process may be practiced with preformed malonaldehyde or succinaldehyde baths, it is often desirable to form the dialdehyde solution in situ, because malonaldehyde and succinaldehyde are relatively storage-unstable. Thus, a dialdehyde-containing bath may be formed by hydrolyzing an aqueous solution of a dialdehyde-forming chemical, such as tetraethoxypropane or diethoxytetrahydrofuran by adding an acid such as sulfuric acid or an alkali such as caustic soda, or in situ by immersing an acid-pickled hide without prior depickling, so as to permit the acid contained in the hide to accomplish the desired hydrolysis and dialdehyde formation. If the hide is pretanned by a mineral tanning agent there is, of course, no more free (pickle) acid present to hydrolyze the donor of the aldehyde. On the other hand, the presence of a mineral tanning agent in the same bath would promote this hydrolysis.

A pH adjustment of the tannage solution to below 7, including the preferred range of pH 2.5-5, is accomplished by adding controlled amounts of conventional acidifying agents, e. g., sulfuric acid or other suitable mineral acid, and alkaline-reacting agents, such as soda ash (so- 7 Example I Tannage with malonaldehyde.-An aqueous solution of malonaldehyde is formed by adding 42 g. tetraethoxypropane to 50 cc. of a sulfuric acid solution, and

shaken until a clear solution results, which now contains malonaldehyde as the product of hydrolysis. This solution, containing approximately 13 g. of malonaldehyde is .adjustedto pH 3.5 with caustic soda and added at once to 500 g. of a pickled cowhide (containing 125 g. of hidesubstance) in abath of 400 cc. of a 5% sodium chloride solution, in which bath the hide has been drummed for /2 hour previously. By half hour feeds of soda ash solutions the pH is gradually raised to 4.25. Altogether about 2.5 g. soda ash are required. The shrinkage temperature rises to 73 C. The hide is washed, split, fat-liquored, and hung to dry. The leather has a pleasing canary yellow color, and has the plumpness and feel of vegetable-tanned leather, being, however, even lighter than vegetable-tanned leather.

Example II Tannage with succinaldehydc.-Example I is repeated with a tanning solution containing, in lieu of malonaldehyde, approximately 15 g. of succinaldehyde. The resulting leather corresponds to that obtained in Example 1, except that its color is light brown, and even softer and plumper than that of Example I.

Example Ill Tanning with dialdehyde formed in Silll.lll(l2 31 g. diethoxytetrahydrofuran are added directly to 500 g. (containing 125 g. of hide substance) of an acid-pickled cowhide in a bath of 400 cc. of a 5% sodium chloride solution in which the hide has been previously drummed for /2 hour. The acid in the pickled cowhide is sufficient to hydrolyze the diethoxytetrahydrofuran to approximately 16.5 g. of succinaldehyde. After five hours drumming the hide is rested for 48 hours. The drum is again run for thirty minutes and then soda ash solution is added in small quantities at half hour intervals, until a pH of 4.8 is reached. At that point a shrinkage temperature of 755 C. is observed. Altogether approximately 1.8 g. soda ash is added. The hides are again rested overnight, run another sixty minutes during which the pH drops to 4.5. The leather is then washed and hung to dry. Without fat-liquor a full and soft leather is obtained. The resulting leather contains approximately 4 percent succinaldehyde combined with the hide substance.

Illb: Example lIIa is repeated, except that a stoichiometrically equivalent amount of tetraethoxypropane is employed in lieu of diethoxytetrahydrofuran. A malonaldehyde solution is formed in situ with the acid contained in the pickled hide. pH adjustments are the same as in Example Illa. The resulting leather is yellower than, but otherwise substantially equal to that obtained in Example IIIa.

Example IV Combination dialdehyde and mineral tannage.An aqueous solution of succinaldehyde is formed by hydrolyzing 14 g. diethoxytetrahydrofuran with 20 cc. of 5% sulfuric acid. This solution is mixed with a basic aluminum sulfate solution prepared by the slow addition of 36 g. soda ash in about 125 cc. water to a solution of 75 g. Al (SO .l8H O in about 300 cc. water .and bringing the resulting solution to a volume of 500 cc. 500 g. of a pickled cowhide are run for one hour with this mixture. After resting overnight the shrinkage temperature of the hide is found to be 79.5 C. The drumming is continued for four hours during which time the hide assumes a tan color. After resting for another night the hide is again run two hours while a total quantity of 10 g. of soda ash in the form of an aqueous solution is added in two feeds, of approximately equal'amounts, one hour apart. The'tan liquor is now drained. The pH of the solution is controlled so as to remain below 7 during the entire tannage process. The tanned hide is washed, set out, split and dried at 115 F. without fat- 'liquoring. The leather obtained is of a pleasing light tan color, strong, much firmer than without the alum, but does not crack on bending or flexing.

In analogy to this example, chromium or zirconium compounds may also be used in place of aluminum sulfate, e. g., basic chromium sulfates or zirconium sulfates of the type ordinarily used by tanneries.

Another donor of malonaldehyde (recently made available in pilot quantities by Kay-Fries Chemicals, Inc., West Haverstraw, N. Y.) namely l,1,3-triethoxy-3-monomethoxypropane does not as readily hydrolyze as tetraethoxypropane and therefore cannot be employed directly in a bath containing pickled hide. However, it can be hydrolyzed prior to use as described in the following Example V.

Example V An aqueous solution of malonaldehyde is formed by adding to 21 g. 1,1,3-triethoxy-3-monomethoxypropane, 10 cc. water containing 4 g. sulfuric acid. After 3-4 minutes a clear solution results which now contains malonaldehyde as the product of hydrolysis. To this solution containing approximately 6 g. malonaldehyde, 20 cc. water and then 9.6 cc. of a solution containing approximately 1 lb./liter caustic soda are added. The mixture had a pH of 5.5. One half of it is stirred into 200 cc. of a 5% sodium chloride solution. The resulting solution is added to 200 g. of pickled cowhide. After drumming for one hour, the other half of the malonaldehyde solution is added. Two and one half hours later the drumming action is interrupted for the night. It is continued for three hours the next morning. Since the pH is found to be 4.5, no alkali is required besides the addition made to the hydrolyzed aldehyde. The hide is washed, fat-liquored and hung to dry. The yellow leather is pliable, full, and strong and shrinks at C.

There are, of course, many other syntheses possible for formation of the aldehydes in question; some of them hydrolyze in presence of pickle acid or pickled pelt, others may not.

It will be readily understood from the foregoing description of my invention and of several examples for carrying the same into practice, that various changes may be made therein without departing from the spirit of my invention, which changes are thus deemed to be encompassed within the scope of my invention, and I therefore desire to claim my invention broadly, as defined by the appended claims.

I claim:

1. In the production of leather from hide, the process of tanning said hide with an aqueous solution of a member of the group consisting of malonaldehyde and succinaldehyde, the pH of said solution being from about 2.5 to about 5.

2. In the production of leather from hide, the process of tanning said hide with an aqueous solution of malonaldehyde, the pH of said solution being from about 2.5 to about 5.

3. In the production of leather from hide, the process of tanning said hide with an aqueous solution of succinaldehyde, the pH of said solution being from about 2.5 to about 5.

4. Process according to claim 2, wherein said aqueous solution of malonaldehyde is obtained by hydrolyzing a hydrolyzable compound which yields malonaldehyde upon hydrolysis.

5. Process according to claim 3, wherein said aqueous solution of succinaldehyde is obtained by hydrolyzing a hydrolyzable compound which yields succinaldehyde upon hydrolysis.

6. In the production of leather, the process of immersing an acid-pickled hide in an aqueous solution of a compound being a member of the group consisting of tetra-alkoxypropane and dialkoxytetrahydrofuran, whereby an aliphatic dialdehyde having not less than three and not more than four carbon atoms in the molecule is formed in situ in said solution, said dialdehyde being a member of the group consisting of malonaldehyde and succinaldehyde, adjusting the pH of said solution to between about 2.5 and about 5, and tanning said hide in said solution While maintaining the pH of said solution between about 2.5 and about 5.

7. Process according toclaim 6, wherein said firstnamed compound is tetraethoxypropane, and wherein said aliphatic dialdehyde is malonaldehyde.

8. Process according to claim 6, wherein said firstnamed compound is diethoxytetrahydrofuran, and wherein said aliphatic dialdehyde is succinaldehyde.

9. In the production of leather from hide, the process of tanning said hide with an aqueous solution of an aliphatic dialdehyde having at least three carbon atoms in the molecule, said dialdehyde being a member of the group consisting of malonaldehyde and succinaldehyde, said solution having a pH between about 2.5 and about 5, and a mineral tanning agent.

10. Process according to claim 9, wherein said mineral tanning agent is a chromium compound.

11. Process according to claim 9, wherein said mineral taning agent is an aluminum salt.

12. Process according to claim 9, wherein said mineral tanning agent is aluminum sulfate.

13. Process according to claim 9, wherein said mineral tanning agent is a zirconium compound.

14. Process according to claim 9, wherein said mineral tanning agent is dissolved in said aqueous solution.

15. In the production of leather from hide, the process of tanning said hide with an aqueous solution of aluminum sulfate and succinaldehyde, said solution having a pH between about 2.5 and about 5.

16. In the production of leather from hide, the steps of immersing said hide in an aqueous solution of a member of the group consisting of malonaldehyde and succinaldehyde, said solution having an initial pH of not less than 2.5 but less than 5, thereafter increasing the pH of said solution to not more than 5, and leaving said hide in said solution until said hide is tanned.

17. Leather tanned in accordance with the process of claim 1, said leather being characterized by pliability, plumpness and resemblance to vegetable-tanned leather.

18. Leather combination-tanned in accordance with the process of claim 9, said leather being characterized by strength, pliability, plumpness and resemblance to vegetable-tanned leather.

References Cited in the file of this patent UNITED STATES PATENTS 1,364,316 Rohm Jan. 4, 1921 2,071,567 Pensel Feb. 23, 1937 2,516,283 Winheim et al. July 25, 1950 2,516,284 Winheim et a1. July 25, 1950 OTHER REFERENCES Gustavson, K. H.: The Chemistry of Tanning Processes, Academic Press, New York, 1956, p. 279.

Winheim and Doherty: Dialdehyde-Resin Tannages, Jour. of Am. Leather Chemical Asso., March 1950, p. 124 relied on.

Fakstorp, Raleigh and Schniepp: Preparation and Reactions of Dialkoxytetrahydrofurans, Jour. of Am. Chem. Soc., vol. 72, 1950, p. 872 relied on. 

9. IN THE PRODUCTION OF LEATHER FROM HIDE, THE PROCESS OF TANNING SAID HIDE WITH AN AQUOUS SOLUTION OF AN ALIPHATIC DIALDEHYDE HAVING AT LEAST THREE CARBON ATOMS IN THE MOLECULE, SAID DIALDEHYDE BEING A MEMBER OF THE GROUP CONSISTING OF MALONALDEHYDE AND SUCCUNALDEHYDE, SAID SOLUTION HAVING A PH BETWEEN ABOUT 2.5 AND ABOUT 5, AND A MINERAL TANNING AGENT. 